SWITCH

Abstract: In a limit switch (1) with a green LED (2) to indicate powering and a yellow LED (3) to indicate actuation, a mode selector (4) with two electro-mechanical microswitches and a slider (7) ensure that the switch (1) can easily and quickly be changed from a mode in which the switch is initially "normally open" to one in which it is initially "normally-closed" and vice versa.

Description: SWITCH The present invention relates to an electro-mechanical switch- One type of electro-mechanical switch typically used in industrial manufacturing machinery has two states, one in which it forms an open circuit and the other in which it forms a closed circuit; the switch can have either state as its initial mode, the other state being its mode once actuated by a mechanical force. The switch has two light-emitting diodes, namely a green LED which is illuminated when the switch is connected to a power supply, and a yellow LED which is illuminated only while a switching operation is occurring. When installing such a switch, wire connections are made between the LED terminals and the switch terminals for powering of the LEDs. If the initial mode of the switch is to be changed, then the wire connections have to be re¬ arranged, this being fiddly work and causing disruption to the other terminal connections. The present invention provides an electro-mechanical switch having two stable positions, one of which is the initial position of the switch and the other is the position of the switch when actuated, the switch having: means to indicate that there is a connection to a power supply; means to indicate when the switch is being actuated; and means to set, by a single manual operation, either of the stable positions as the initial position of the switch. In this way, the switch incorporates a mode selector so that the switch can be installed in the appropriate mode (or its mode can be changed after installation) quickly, easily and without disruption to the other terminal connections. The set means may comprise a slider mechanism, a push-button mechanism, a pivoting action or any other appropriate arrangement. Preferably, the set means, in operation, effects a change of the electrical connection(s) of the supply-indicator means and/or the actuation- indicator means within the switch. The set means may comprise cam means movable between one location, in which one of the stable positions constitutes the initial position of the switch, and another location in which the other of the stable positions constitutes the initial position of the switch. Preferably the set means comprises electrical switch means located between the terminals of the electro-mechanical switch and the indicator means. The set means may include a locking, securing or fastening member to hold the set means in a given mode. In order that the invention may be more readily understood, a description is now given, by way of example only, reference being made to the accompanying drawings in which: Figure 1 is a perspective view of a limit switch embodying the present invention; Figure 2 is a plan view, partly sectioned, of the switch of Figure 1; Figure 3 is a circuit diagram of part of the limit switch of Figure 1; Figure 4 is a view of the terminal of the limit switch of Figure 1. Figures 1 and 2 shows a limit switch 1 of the type having a green LED 2 to indicate when the switch is powered and a yellow LED 3 to indicate whenever the switch is actuated (the LED's not being visible in Figures 1 or 2). Switch 1 has a mode selector 4 with two electro-mechanical microswitches 5 and 6 and a slider 7 with cam surfaces 8 and 9 engageable against the levers 10 and 11 of microswitches 5 and 6. LEDs 2, 3 and microswitches 5 and 6 are connected to a pcb circuit as shown in Figure 3, the circuit including protection diodes 12 and 13 to prevent the LEDs being damaged if the limit switch is wired up incorrectly, circuit terminals CTi, CT2, CT3, CT and CTA being linked in use to switch terminals STi, ST2, ST3, ST 4 and STA in a manner to be described later, with Figure 4 showing how switch terminals STi, ST2, ST3, ST 4 , and STA of limit switch 1 are wired up to the external circuit in which switch 1 operates. The limit switch 1 must be connected so that terminals STi and ST3 are the Hve side of the switch (i.e. input) and terminals ST2 and ST 4 are the isolated side (i.e. output). The switch terminals are hard wired to the two microswitches 5 and 6, one microswitch for the input terminals STi and ST3 and the second for the output terminals ST2 and ST 4 . These microswitches are operated by bias cams 8 and 10, to allow their outputs to be connected to either the "normally open" terminals STi, ST2 or "normally closed" terminals ST3, ST of the limit switch 1. Microswitches 5 and 6 connect the LED's diagonally across the limit switch 1 with the green LED 2 always being connected to the input side, and the yellow LED 3 always to the output. When the mode selector 4 is such that the switch in the initial position is "normally open" i.e. microswitches 5, 6 are set up as shown in Figure 3, the green LED 2 is connected via CTi to teπninal STi and is hence live with green LED 2 illuminated, while the yellow LED 3 is connected via CT 4 to terminal ST and hence the yellow LED 3 is not illuminated. As long as power is connected, then the green LED 2 is lit. The "normally closed" circuit should be used for a signal supply. Only when the switch has been activated or switched will te * raιinal CT (and hence the yellow LED 3) be connected to the signal supply and therefore yellow LED 3 be lit. Thus the green LED 2 is lit permanently and the yellow LED 3 goes on and off as the switch is operated and then returned to the initial position. If the mode selector 4 is altered so that the initial position of the switch is a "normally closed" situation, then the microswitches are set up in the opposite way from that shown by in Figure 3, green LED 2 is connected via CT3 to ST3 which is live so that green LED 2 is illuminated, while yellow LED is connected, via CT2, to ST2 which is isolated so that yellow LED 3 is not illuminated. Only when the switch has been activated or switched will terminal CT2 (and hence the yellow LED 3) be connected to the signal supply and therefore yellow LED 3 be lit. By connecting the outputs of the two LED's to a fifth terminal CTA which acts as a return or ground, then the LED's still operate even if somewhere downstream of the limit switch there is a break in the circuit. This prevents users assuming the supply to the limit switch 1 is off and being electrocuted.

Claims: CLAIMS 1. An electro-mechanical switch having two stable positions, one of which is the initial position of the switch and the other is the position of the switch when actuated, the switch having: means to indicate that there is a connection to a power supply; means to indicate when the switch is being actuated; and means to set, by a single manual operation, either of the stable positions as the initial position of the switch. 2. A switch according to Claim 1, wherein the set means, in operation, effects a change of the electrical connection(s) of the supply- indicator means and/or the actuation-indicator means within the switch. 3. A switch according to Claim 1 or 2, wherein the set means comprises cam means movable between one location, in which one of the stable positions constitutes the initial position of the switch, and another location, in which the other of the stable positions constitutes the initial position of the switch. 4. A switch according to any preceding Claim, wherein the set means comprises electrical switch means located between the terminals of the electro-mechanical switch and the indicator means. 5. A switch according to any preceding Claim, wherein the set means includes a locking, security or fastening member to hold the set means in a given mode. 6. A switch according to any preceding Claim, wherein an output of at least one of the indication means is connected to a return or a ground terminal.

Inventors: TRICKETT PAUL, TRICKETT, PAUL
Applicants: HONEYWELL CONTROL SYST, TRICKETT PAUL, HONEYWELL CONTROL SYSTEMS LIMITED, TRICKETT, PAUL
Application year: 1994
Main classification: H01H11
IPC codes: H01H11